There are already dedicated buttons for volume, mute, play/pause, CD eject further above the keyboard.
If that's the case, then it is silly to map those to function keys.
You seriously change the brightness of your screen or change the volume of your music more than you edit?
At home, yes. At work, no, but I do those things more than I use function keys for other things. I have about 4 function keys mapped for things I do semi-regularly in my editor/email client, and that's it. All my other key-strokes (aside from the Esc key; yay vim!) are contained within the regular typewriter keys. And I'm one of those weirdos that maps the caps-lock to Ctrl, and uses a dvorak layout (on a qwerty labeled keyboard).
Admittedly your *nix type tools are less function key oriented. In a Windows world though....
This is probably the key (haha).

In vim, the only pre-mapped function key is F1 for help, but I use ':help' instead. In Firefox, I use '/' to search, and ctrl-R to refresh the page. I didn't even know there were function key equivalents.